chambers absorber
TRANSCRIPT
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Copyright 2003, ETS-Lindgren, L.P.
An Introduction to RFAnechoic Chamber
Technology
Vicente Rodriguez, Ph.D.
ETS-Lindgren
1301 Arrow Point Dr.
Cedar Park, TX, 78613
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SUMMARY
The Chamber Family
Absorber Materials
The EMC Chamber The antenna Chamber
Tapered and Rectangular.
RCS chambers References
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Chamber Types: Two Main Families
EMC testing Properties: Semi-free space or
half free space
Absorber: FS-1500,1000,600,400
(polyurethane) and FS-
1250,600,400 PS and EMC-24,(for High frequency applications
other absorber may be used).
Design tools: In-House Software
Std. Doc: ANSI C63.4-1992/1998;
EN50147-2 (semi-anechoic),-
3(fully anechoic),-1(shielding
test); VCCI V98.3 (Japanese);
RCS and Antenna. Properties: Fully anechoic.
Absorber: EHP series absorbers
RCS: mostly military
applications, is a chamber to
measure radar cross section of atarget
Antenna: military and
commercial, these are chambers
to measure the radiation pattern
of a radiator, could be an
antenna or an antenna plus other
system.
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The Absorber Family 1
Microwave
Pyramidal absorber.
EMC and EHP series
Electric Losses
Preferred technology
for High frequencies
It can be used for low
frequencies if size(length) is increased
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The Absorber Family 2
Ferrite Tile .
Magnetic Losses
Preferred technology
for Low frequencies (up
to 1GHz), it has lowprofile.
It cannot be used for
high frequencies
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The Absorber Family 3
Hybrid Absorber .
Electric and Magnetic Losses
Preferred technology for EMC
Applications. foam has to havespecial formula for good
matching with ferrite tile at the
bottom. At High frequencies its
performance is not as good as
MW pyramid of equal size. Flattop causes undesired reflections
at MW range.
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The Absorber Family 4
Flat laminate .
Electric Losses
Preferred technology for
laboratory set ups. It is asandwich of different foams.
About 20dB absorption as
frequency increases.
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The Absorber Family 5
Wedge and pyramid
Electric Losses
A variant of pyramidal
absorber wedge does not showbackscattering. Preferred
technology for QZ treatment
and for RCS chambers.
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Copyright 2003, ETS-Lindgren, L.P.
Popular types of absorber have constitutive parameters of:
12
1
jr
r
Non magnetic material
Low permittivity with losses
We will study how the electromagnetic wave behaves as isincident on to a wall of this type of absorber.
This material isvolumetrically
loaded having
the same
constitutive
parameters
through the
volume of the
pyramid
Pyramidal Absorber Theory (Example)
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At the tip of theabsorber
The wave
impedance is that
of air
At the base of the pyramidThe wave impedance becomes
oZ 0377
o
jZ 3.1325212
377
Along the length of thepyramid the waveimpedance falls betweenthose two values.
Pyramidal Absorber Theory (Example)
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Pyramidal Absorber Theory (Example)
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dBee
jjjj
x
m
Np
o
380123.02235.0
35.046.1"'
1.022221.0
2
1.022
Letsassume a
length of
30cm
The
wavelength
at 3GHz is
10cmAnd at
10GHz is
30mm
Lets approximate by saying that the
pyramid is equivalent to a solid mediumof 1/3 the height
For 3GHz
Wavelength
at 3GHz
Approximate thickness of
equivalent solid material
Pyramidal Absorber Theory (Example)
C i h 2003 ETS Li d L P
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Copyright 2003, ETS-Lindgren, L.P.
dBee
jjjj
x
m
Np
o
1271029.4
7335.0
35.046.1"'
71.07322
03.02
03.0
22
Lets approximate by saying that the
pyramid is equivalent to a solid mediumof 1/3 the height
For 10GHz
Wavelength
at 3GHz
Approximate thicknessof equivalent solid
material
In practice the reflection coefficient may not be as small as this but it will be significantly
Smaller than at 3GHz
Pyramidal Absorber Theory (Example)
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EMC Chamber
Design is guided by thestandards and the test that thecustomer is going to perform.Frequency range is from 30 to1000MHz
At what distance is themeasurement (3m, 5m,10m)?Are we testing immunity oremissions?
The chamber must perform asif it was an infinite groundplane in an infinite open space
NSA is a measurement of howclose we are to this goal.
Std.Docs call for NSA beingwithin +- 4dB of the theoretical.
4m
1m
1,3,5,10m
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EMC Chamber
A
B
D Tx1
Tx2
QzdQzs
abs
abs
abs
Rx2
Rx1
Dsin()
mQzsmRxwhereabsQzsRxQzdDA
1,21:212
Rx1 can be a minimum of 1.5m
It is desirable that > 0 so that
reflections from the side walls
Do not arrive in phase to the test
area.
There are some rules that can be
applied when sizing an EMC
Chamber once the test distance
and the quiet zone size are
known
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Copyright 2003, ETS-Lindgren, L.P.
EMC Chamber
The FCC asks that the
performance of that anechoic
chamber matches that of an out
door range.
The Normalize Site Attenuation
(NSA) is measured.
Another common measurement
for qualification is the field
uniformity measurement
A
H
D
Tx1
1m
abs
abs
14 meter scan
1.5m
2m
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EMC Chamber
A typical standard will have wording similar to this:
ANSI C 63.4-1992 5.4.2, Alternate test Sites: Measurements can be
made at a location other than an OATS, ... Provided that the alternate site
meets the site attenuation requirements of 5.4.6 over the volume occupied
by the EUT, and the ground plane requirements of 5.4.3
What this means is that it must be shown that the
chamber performs like an infinite ground planewith no obstructions anywhere.
Chamber Validation Requirements
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Vertical Polarization VNSA
EMC Chamber
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Horizontal Polarization HNSA
EMC Chamber
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Testing the Uniform Area according EN 61000-4-3. For chambers where immunity measurements will
be performed it may be required to test the FU according to a given standard. this will show that thereflections from the wall do not affect the field.
0.5 m
0.5 m
0.8 m
This plane includes the uniform area, 12 from 16 points of E-Field are within +6/-0 dB.
EMC Chamber
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Copyright 2003, ETS Lindgren, L.P.
EMC Chamber: Partially linedchambers
Mil Std chambers and some other aircraft
and SAE EMC standard documents call for
partial absorber treatment chambers. Frequencies for use start in the 100 of
MHz.
Not looking for a half free space.
Absorber is loading the cavity (chamber) to
reduce any resonant behavior. EMC24 absorber is enough for these
applications.(A pyramidal specially loaded
absorber)
EUT Bench
1m
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Copyright 2003, ETS Lindgren, L.P.
EMC Chamber: Mil Std Chamber Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,
EUT size determines the size of the chamber. The sketches bellow show the
standard MIL-STD chamber offered by ETS-Lindgren.
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py g , g ,
Mil Std 461E
What is it? Department of Defense: Requirementsfor the control of electromagneticinterference characteristics of
subsystems and equipment So it is a complete Standard for all
different EMC measurements
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py g , g ,
Mil Std 461E
Mil Std 461 E came to be inAugust 20 1999
It superseding bothMil Std 461D and Mil Std 462DWhich passed away(rest in peace)
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py g g
Mil Std 461E
Mil Std 461EIs made ofmany parts(which one
are YOUinterestedin)
Conducted
Radiated
Emissions
Susceptibility
Emissions
Susceptibility
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Mil Std 461E Conducted
Conducted
Emissions
Susceptibility
CE 101
CE 102
CE 106
CS 101
CS 103
CS 104
CS 105
CS 109
CS 114
CS 115
CS 116
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Mil Std 461E Conducted
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Mil Std 461E ConductedEmissions
CE
CE 101
CE 102
CE 106
Conducted Emissions, power leads 30HZ-10KHz
Conducted Emissions, power leads 10KHz-10MHz
Conducted Emissions, Antenna terminal, 10KHz to40GHz
No chamber requiredShielded roomrecommended.
LISN, receivers,Ocope, data
recorders, sig gens,Current probe, etcare part of therequired Equipment
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Mil Std 461E Conducted
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Mil Std 461E ConductedSusceptibility (Immunity)
CS
CS 101CS 103
CS 104
CS 105CS 109
CS 114
CS 115CS 116
Conducted Susceptibility, Power leads, 30Hz, to 150KHz
Conducted Susceptibility, Antenna Port, Intermodulation, 15KHz to10GHz
Conducted Susceptibility, Antenna Port, rejection of Undesiredsignals, 30Hz to 20GHz
Conducted Susceptibility, Antenna Port, Cross-modulation, 30Hz to20GHz
Conducted Susceptibility, Structure Current, 60Hz to 100KHz
Conducted Susceptibility, Bulk Cable Injection, 10kHz to 200Mhz
Conducted Susceptibility, Bulk Cable Injection, Impulse excitation
Conducted Susceptibility,Damped Sinusoidal transients, cables andpower leads, 10KHz to 100MHz
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Mil Std 461E Radiated
Radiated
Emissions
Susceptibility
RE 101
RE 103
RE 105
RS 101
RS 103
RS 105
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Mil Std 461E Radiated
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Mil Std 461E RadiatedEmissions
RE
RE 101
RE 102
RE 105
Radiated Emissions, Magnetic Field, 30Hz to 100KHz
Radiated Emissions, Electric Field, 10KHz to 18GHz
Radiated Emissions, Antenna Spurious andharmonic Outputs, 10KHz to 40GHz
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Mil Std 461E Radiated
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Mil Std 461E RadiatedSusceptibility (Immunity)
RE
RS 101
RS 103
RS 105
Radiated Susceptibility, Magnetic Field, 30Hz to 100KHz
Radiated Susceptibility, Electric Field, 2MHz to 18GHz
Radiated Susceptibility, Transient Electromagneticfield
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Mil Std 461E Where do we
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Mil Std 461E Where do wetest?
Paragraph 4.3.2
Paragraph 4.3.2.1
To prevent interaction between the EUT and the outsideenvironment, SHIELDED ENCLOSURES will be usuallyrequired for testing
RF absorber material shall be used when performing
RE and RS testing inside a shielded enclosureThe RF absorber shall be placed above, behind and onboth sides of the EUT, and behind the radiating orreceiving antenna
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The Absorber Family
EMC-24
Mil Std 461E requirementsTABLE I page 10
6dB absorption 80Mhz to 250Mhz10dB absorption 250Mhz and above
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Mil Std Chamber side view Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,
EUT size determines the size of the chamber. The sketches bellow show the
standard MIL-STD chamber offered by ETS-Lindgren.
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Mil Std Chamber Side View Mil Std 461 Defines the size of the chamber in terms if the EUT being measured,
EUT size determines the size of the chamber. The sketches bellow show the
standard MIL-STD chamber offered by ETS-Lindgren.
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Mil Std Chamber RE and RS
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Mil Std Chamber RE and RSEquipment
RE101
RECOMMENDED REQUIRED
CHAMBER
EMCO 3725-2MCurrent Probe
EMCO 4-TR
EMCO 7604
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Mil Std Chamber RE and RS
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Mil Std Chamber RE and RSEquipment
RE103
REQUIRED
CHAMBER
EMCO 3725-2M
EMCO 4-TREMCO 7-TR
EMCO 3301BEMCO 3110B
EMCO 3106
EMCO 3115
MIL STD 461E does not longer accept Log Periodic and spiral Logs onlydouble ridge horns above 200MHz
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Mil Std Chamber RE and RS
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Mil Std Chamber RE and RSEquipment
RS101
RECOMMENDED REQUIRED
CHAMBER
EMCO 3725-2MCurrent Probe
EMCO 4-TR
EMCO 7605/7606
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Mil Std Chamber RE and RS
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Mil Std Chamber RE and RSEquipment
RS103
REQUIRED
CHAMBER
EMCO 3725-2M
EMCO 4-TREMCO 7-TR
EMCO 3301BEMCO 3109
EMCO 3106
EMCO 3115
MIL STD 461E does not longer accept Log Periodic and spiral Logs onlydouble ridge horns above 200MHz
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Mil Std Chamber RE and RS
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Mil Std Chamber RE and RSEquipment
RS103
paragraph 5.19.4, states that an accepted method is the mode tunedreberveration chamber, the range is 200MHz to 40GHz, for the reverb logperiodics can be used since pattern is no longer an issue
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CISPR 25
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CISPR 25
Limits and methods of measurement of radio
disturbance characteristics for the protection ofreceivers used on board vehicles
This means that we measure the emissions that would
affect any receiver in the vehicle. Is another self
immunity standard, of how vehicle receivers areimmune to radiated emissions from its own systems
SAE J 551-4 and SAE J 1113-41 are equivalent
standards
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CISPR 25
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CISPR 25
Covers the frequency range from 150KHz- 1000MHz
When an absorber lined chamber is used theabsorption of the material has to be better than 6dB for
the range 70MHz and up.
For the chamber testing of subsystems a monopole is
used for the range 150KHz to 30MHz, for 30MHz to200MHz a biconical antenna is used, the log periodic is
used for the range 200MHz-1000MHz. For equipment
testing a TEM cell can be used.
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EMC Chamber: CISPR 25 Chamber
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EMC Chamber: CISPR 25 Chamber The CISPR-25 calls for reflectivity in the EUT area to be better
than 6dB.
There is no method for testing this.
Normal incidence performance of absorber is the best way todetermine the reflectivity in the area given the test geometry
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EMC Chamber: CISPR 25 Chamber
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EMC Chamber: CISPR 25 Chamber A recommended practice is to map the field along the cable
harness although the standard does not mentions anythingabout any chamber validation method. This method can helpcompare the results in two different chambers.
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CISPR 25 Chamber Side View (Bicon)
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CISPR 25 Chamber Side View (Bicon)
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CISPR 25 Chamber Side View (Bicon)
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CISPR 25 Chamber Side View (Bicon)
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CISPR 25 Chamber Monopole Testing
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CISPR 25 Chamber Monopole Testing
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EMC Chamber: CISPR 25 Chamber
Apart from component testing the CISPR 25 rooms could
accommodate some vehicle testing if the floor is reinforced.
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CISPR 25 TEM Cells
Additionally CISPR 25 allows for testing ofequipment in TEM cells and other TEM likedevices
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Automotive Testing:
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Automotive Testing:A Short Introduction 50
Every manufacturer has its ownrequirements (usually very difficult to
meet).
Automotive standards are actually
rather simple.
The most common are SAE, ISO and95/54 EC. These usually are copies of
each other with small difference.
The previous slides look at the FACT
25 chamber which can be used for
automotive component testing for allthese standards.
A short introduction to emission testing
of whole vehicles is presented now
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Automotive Testing:A Short Introduction
51
The 10m emission testing
locates the antenna 10m from
the outer shell of the vehicle
The antenna is not scan but
located at 3m height. (For 3m
testing the antenna is located at1.8meters.
Both sides of the vehicle and
both polarizations are tested
10 meters
LPDA
BICONICAL
HORN
10 meters
10 meters
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Automotive Testing:
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Automotive Testing:A Short Introduction 52
The antenna is to be
in line with the
middle point of the
engine compartment.
A two antenna
position chamber
makes the test much
easier
Plane of longitudinal symmetry
10 meters
mid point of engine
compartment
Antenna in line with
mid point of engine
compartment
10 meters
The antenna not in use is set
At a different polarization to
reduce coupling between antennas
10 meters
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EMC Ch b
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EMC Chamber
There are a lot of different Standards in EMC. When a
different standard request appears the RF engineer mustanalyze the requirements of the standard and
recommend a proper solution.
Also customers may have their own special requirements.
Their company may have internal requirements fortesting. RF engineering analysis must be conducted to see
how to meet these requirements (or if is even possible to
meet them.
Most chambers are required to meet several standards.
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A Ch b R i
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The purpose of these chambers is to measure the radiation
pattern and characteristics of a radiator
Antenna Chamber: Requirements
Requirements
1. Frequency range:
2. Far field Requirement:
3. Quiet Zone Size:
This may determine if a tapered or
rectangular chamber should be used
Directly related to the previous
requirement since is related to the
wavelength at the lowest frequency:
The far field distance will determine
the path length and hence the
chamber length.
freq.lowest
22
dSd
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A t Ch b R i t
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Antenna Chamber: Requirements
Requirements
3. Quiet Zone Size:
4. Source Antenna Selection:
Test region where the level of
reflected energy is equal or smallerthan certain specified value
Must be large enough to encompass
the largest antenna being measured:
It also determines the size of the
chamber, the rule of thumb is that
width and height of chamber be at
least 3 times the Qz diameter or side.
Can be:
SphericalCubical volume
Cylindrical
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Antenna Chamber: Requirements
Requirements
4. Source Antenna Selection:
5. Back wall
Considerations:
Rectangular chamber: the source antennamust have a pattern that illuminates the whole
Qz while avoiding the side walls.
Tapered chambers: Small antennas better.
15dB gain at least. No LPDA as phase center
moves.
Absorber normal incidence must be at least
equal to Qz level, avoid lights, cameras and
doors, ( for both rectangular and tapered.)
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Antenna Chambers: Rectangular and
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Rectangular Free Space condition
What Antennas can be
measured? Omni-directional
and directional.
Tapered Quasi-free Space.
Absorber treatment is used to create a
far field free space behavior of the
waves at the location of the antenna
under test.
Lower frequency antenna patterns can
be measured
It can be used for High frequency
testing but positioning of the source
antenna is critical
Antenna Chambers: Rectangular andTapered
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Antenna Chambers: Rectangular and
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Antenna Chambers: Rectangular andTapered
CRITERIA RECTANGULAR TAPERED
Antenna Patterns Poor at LF, good at
mid and HF
Good at Low Mid and
High F
Source placement Not critical Critical at HF
Source antenna Limited by Far field 15dB directivity
Axial ratio 25dB
Swept frequency
measurements
Ideal configuration Not recommended
Amplitude taper (Qz) Freq. independent Freq. Dependent
Phase deviation (Qz) Freq. independent Freq. Dependent
Boresite error low Potentially high
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A t Ch b R t l I
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Antenna Chamber Rectangular I
Pyramid
Top (or side view)
Pyramid
Pyramid
A
B
Pyramid
Qz
2
Path length
depthabsorber24
yaccuratellmoreor3
depthabsorber2
freq.lowest
2freq.lowest
2
QzB
QzB
PL
QzPLAd
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A t Ch b R t l II
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Antenna Chamber Rectangular II
QzPath length
Design of Rectangular chambers:
The application of the chamber will determine the Qz size and the Path length and
with it the size of the chamber
Determining the specular performance:
Based on the thickness of absorber the
behavior at different incident angles can be
computed.
Assume a chamber with: width B; pathlength L; Qz radius r, then
rBd
Ld
dL
)(tan
)(tan
1
1
d
Br
It is desirable to have
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Antenna Chamber Rectangular III
QzPath length
With the value of it is possible (based on the thickness of the absorber in terms of
wavelengths) to determine the expected reflectivity.
With the known directivity of the antenna and
The knowledge of it is possible to compute
The gain of the antenna in that direction
The reflection at the edge of the quiet zone
Is given by:
Where R is the absorber reflectivity and G is the gain of the source antenna
atat GRQz tyreflectivi
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Antenna Chamber: The Absorber
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Treatment
Back wall(receive end wall)
Side wall
Normal Reflectivity better than QZ level
Oblique incidence Reflectivity with off
main beam gain better than QZ level
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Antenna Chamber: The Absorber
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Treatment
Side wall absorber is only needed on those areas
where a specular reflection exists between thesource and the QZ
Everywhere elseshorter absorber canbe used
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Antenna Chamber: The Absorber
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Treatment
Transmit end wall absorber can have a reflectivity
that when added to the front to back ratio of thesource antenna it meets the required QZ level
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Antenna Chamber: The Absorber
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Antenna Chamber: The AbsorberTreatment
1. For a given pyramid element size chosen there is no expected backscattering
component. The scattered field is a sum of all the possible grating lobe waveswhich propagate in different directions, Only those where the following conditionis satisfied contribute to the scattering at a distance [*]
2. For m=0 and n=0 we have specular reflection only. For higher order modes topropagate we see that the period of the structure has to be larger than thewavelength
3. [*] W. Sun, C. BalanisAnalysis and Design of Periodic Absorbers by Finite-DifferenceFrequency-Domain Method report No. TRC-EM-WS-9301 TelecommunicationsResearch Center, Arizona State University, Tempe, AZ 1993.
2
22
22k
D
nk
D
mk
x
i
x
y
i
y
DD
22
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Antenna Chamber: The Absorber
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Treatment
At high frequencies the antenna under test may re-
scattered the backscattered energy from thepyramidal absorber surrounding it
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Antenna Chamber: The Absorber
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Antenna Chamber: The AbsorberTreatment
1. Traditionally in RCS chambers the backscatter of the side walls
(and ceiling/floor pair) is to be reduced using Wedge. By usingwedge around the QZ section of the chamber we can improvethe quality of the measurements at high frequencies
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Antenna Chamber: The Absorber
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Treatment
Pyramid
Top (or side view)
Pyramid
Pyramid
A
B
Pyramid
Qz
2Wedge
Wedge
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Far Field and QZ
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Far Field and QZ
QZ )(xf Absorber reflectivity, chamber size,Gain of source antenna
FF )(xf Antenna size and frequency of operation
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Far Field and QZ
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Far Field and QZ
QZ reflectivity can be found. For any frequency.But that does not imply that the whole QZ is in the FF
)(xf
Knowing the chamber size, absorber layout,Gain of source antenna, and QZ diameter
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Far Field and QZ
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Far Field and QZ
If the path length is fixedThat it is possible todetermine what is the QZdiameter that will be in thefar field assuming
illumination by sphericalwaves from a point sourceat the location of thesource antenna
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Far Field and QZ
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Far Field and QZ
ANECHOIC CHAMBER DESIGN SUMMARY
Job # : 0 Customer: XXXXXXXXXXXXXX
19-Aug-03 Location: XXXXXXXXXXXXXX
SPHERICAL Quiet Zone 2 ft. dia.
Receive Endwall Abs Size = EHP-24 EHP- 24 CL
Specular Region Abs Size = EHP-18 EHP- 18 CL
Dimensions are (LxWxH)= 20 x 10 x 10
Path Length (ft) = 13
RCV Ant. Discrimination added
Angle of Incidence = 57.3 Degrees
SIDE WALLS, FLOOR/CEILING CALCULATIONS FOR
ANECHOIC CHAMBER QUIET ZONE PERFORMANCE
WORST CASE
Frequency Wavelength Thickness/ Absorber Spec 5 10 15 18
(MHz) (inches) Reflectivity (-DB)
1000 11.82 1.52 24 25 25 27 35 38
2000 5.91 3.05 33 34 36 43 452500 4.73 3.81 35 35 37 39 47 51
7000 1.69 10.66 48 50 49 51 55 55
8000 1.48 12.18 50 50 52 55 55
9000 1.31 13.71 52 50 51 53 55 55
14000 0.84 21.32 53 52 53 55 55
18000 0.66 27.41 53 50 52 53 55 55
Source Antenna Gain (DB)
GUARANTEED PERFORMANCE
So for a given size
Chamber we canprovide the QZreflectivity for a set offrequencies anddifferent sourceantenna gains.
The example shows a
20ft by 10ft by 10 ftchamber with 18 and
24 absorber and a 2ft
diameter QZ.
Copyright 2003, ETS-Lindgren, L.P.
Far Field and QZ
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Far Field and QZ
But of the given 2ft ofQZ and for a fixed 13ftpath length onlysmaller spheres are inthe FF of the sourceantenna
freq (MHz) c lambda QZ ft QZ m PL m PL ft
1000 3.00E+08 0.3 2.5 0.762 3.87096 132000 3.00E+08 0.15 1.8 0.54864 4.013411 13
3000 3.00E+08 0.1 1.45 0.44196 3.906573 13
4000 3.00E+08 0.075 1.25 0.381 3.87096 13
6000 3.00E+08 0.05 1.05 0.32004 4.097024 13
8000 3.00E+08 0.0375 0.9 0.27432 4.013411 13
10000 3.00E+08 0.03 0.8 0.24384 3.963863 13
18000 3.00E+08 0.016667 0.6 0.18288 4.013411 1340000 3.00E+08 0.0075 0.4 0.12192 3.963863 13
Copyright 2003, ETS-Lindgren, L.P.
Antenna Chamber Tapered I
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Antenna Chamber Tapered I
Top (or side view)
Pyramid
Pyramid
Pyramid
Qz
2
Wedge
Wedge
Wedge
Pyramid
Tapered chamber concept was develop to avoid the deficiencies of the Rectangular
chambers at low frequencies
At frequencies below 500MHz: Horns are no longer an option (very large).Less efficient antennas must be used.
The thickness of the side wall absorber has to be
increased to allow for good
performance (and the chamber size
increases to accommodate absorber).
Tapered chambers do not eliminate the specular reflection. The specular region is locatedclose to the aperture of the source antenna.
The resulting Quiet Zone amplitude
and phase tapers approach those
Expected in free-space hence the term
QUASI-FREE-SPACE
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Antenna Chamber Tapered II
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Antenna Chamber Tapered II
Top (or side view)
Pyramid
Pyramid
Pyramid
Qz
2
Testing antenna
Std Horn or ridge horn dipole minimum, No Log Periodic (phase center moves
away from the side walls)
Wedge
Wedge
Wedge
Pyramid
This area absorber is critical
This areaabsorber is less
than
thickness
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Antenna Chamber Tapered III
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Antenna Chamber Tapered III
Top (or side view)
Pyramid
Pyramid
Pyramid
Qz
2
Wedge
Wedge
Wedge
Pyramid
1. Qz needs to be 1/3w clear from the sides
2. half wavelength clear from absorber tips
3. Apex angle less than 28 deg. Hence length
depthabsorber24
yaccuratellmoreor3
freq.lowest
QzB
QzB
o
LF
B
Length
28
2width)(absorber2
tan
2
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RCS Chambers I
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RCS Chambers I To measure Radar cross
section
We only want reflection
from the target
Wedge is used on part of
the walls, ceiling and floor
to reduce reflections from
incidence on the flat part
of the pyramids.
The target illumination
mechanism changes
depending on frequency
and type of radar.
Pyramid
Pyramid
Top (or side view)
Wedge
Wedge
Pyramid
Pyramid
A/3A
B
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The RCS Chamber
To measure Radar cross section (That is, the energy that bounces back froma target to the source of the original incident signalMONOSTATIC, or to a
receiver located at a different pointBISTATIC)
We only want reflection from the target coming back
Wedge is used on part of the walls, ceiling and floor to reduce reflections
from incidence on the flat part of the pyramids.
Copyright 2003, ETS-Lindgren, L.P.
RCS Chambers II
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RCS Chambers II
Reflection of the back wall willlimit how small of a RCS can be
measured in the chamber.
Assuming a good targetillumination system is used theRCS of the back wall can begiven by the RCS of an infinite
reflective wall
Minus the normal incidencereflectivity of the absorberplaced on the back wall.
2DRCS
D
Copyright 2003, ETS-Lindgren, L.P.
RCS Chamber: Target Illumination
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RCS Chamber: Target Illumination
Always try to reduce the any energy going to
the side walls.
Two antennas (one receive one transmit)
One antenna (receive and transmit)
Compact range reflector
Top (or side view)
Pyramid
Wedge
Wedge
Pyramid
Pyramid
A/3
A
B
Pyramid
Top (or side view)
Pyramid
Wedge
Wedge
Pyramid
Pyramid
A/3
A
B
Pyramid
Top (or side view)
Pyramid
Wedge
Wedge
Pyramid
Pyramid
A/3A
B
Pyramid
Copyright 2003, ETS-Lindgren, L.P.
References
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References
Brownell F. P. Radio Frequency Anechoic
Chambers lecture materials, Microwave AntennaMeasurement short Course, fb ConsultantsCamarillo,California.
Kraus J. D.Antennas, 2d Ed. McGraw Hill:
Boston, Ma, 1988.
Balanis C. A.Antenna Theory: Analysis anddesign, 2d Ed, Wiley: New York, NY, 1997.
Liu K. Private Communication